1. Field of the Invention
The present invention relates to a photoresist composition and a method of forming a pattern using the same, and more particularly, to a photoresist composition having a thermal curing agent and a method of forming a pattern using the same.
2. Description of the Related Arts
Flat panel display devices have become increasingly popular because they are thin, light, and have a low power consumption characteristic.
Among flat panel devices, liquid crystal display (LCD) devices have been widely utilized because in addition to the above advantages LCD devices are capable of displaying a high quality image. LCD devices are widely used as computer monitors and more recently as television units.
As LCD devices become larger, manufacturing becomes more complex. One reason is because the need for an enlarged glass, and the need to use photoresist composition satisfying new process conditions, such as processes for fabricating the fine featured patterns of circuits.
LCD devices are generally classified into reflection type and transmission type. The power consumption of the reflection type LCD device is lower than that of the transmission type LCD device and an image displaying quality of the reflection type LCD device at the outdoor is better than that of the transmission type LCD device. In addition, a separate light source such as a back light assembly is not required for the reflection type LCD device.
Because there is no backlight assembly, the display image of the reflection type LCD device is not bright and a correspondent minute display and color display are also not sufficient bright. Accordingly, the use of the reflection type LCD device is limited for displaying numerals and simple characters. If reflection type LCD devices are to be used for various electronic display devices, the reflection efficiency, and the brightness of the minuteness and coloring need to be improved.
For the reflection type LCD device, the brightness is improved by combining two techniques of increasing a reflecting efficiency of a reflecting electrode and a fine aperture efficiency. U.S. Pat. No. 5,610,741 issued to Naofumi Kimura discloses and proposes a method of improving reflecting efficiency by forming minute irregularities on the reflecting electrode.
An important point for the manufacture of the minute irregularities is the formation of an embossing pattern by using an organic insulating layer. The shape of the embossing pattern is dependent on a curing temperature thereof as well as a characteristic of a pattern forming material. Accordingly, when the reflowing characteristic of the embossing pattern can be controlled according to the temperature, a desired pattern can be obtained.
An embossing pattern is generally formed by a method described below. First, a photoresist composition is coated on a substrate by a common coating method such as dipping, spraying, rotating, and spin coating to form a photoresist layer.
The coated photoresist layer is heated to about 80-130xc2x0 C. (soft bake) to evaporate the solvent. The formed photoresist layer is selectively exposed to light such as ultraviolet by using a mask to form an exposed portion, wherein the photoresist layer becomes an alkali-soluble resin and dissolves into a developing solution during a subsequently implemented developing process. The exposed layer is dipped into the aqueous alkaline developing solution and is stood still until almost the exposed portion of the photoresist layer is dissolved. As for the developing solution, an aqueous solution including alkaline hydroxide, ammonium hydroxide, tetramethyl ammonium hydroxide, and the like can be used.
After completing the dissolution of the exposed portion, the substrate is taken out of the developing solution. Then, a heat treatment is performed to increase an adhesiveness and a chemical-resistance of the photoresist layer. This process is called a hard bake process. This heat treatment is performed at a temperature range of about 100-250xc2x0 C. Through a completion of the heat treatment, an embossing pattern having a desired shape can be obtained.
On the embossing pattern, a reflecting layer is formed by a vacuum deposition process using aluminum, nickel, etc. Then, the reflecting layer is formed to have irregularities along the shape of the underlying embossing pattern to increase the reflecting efficiency of the reflecting layer.
However, the organic insulating layer of the embossing pattern reflows during performing a thermal curing process such as a heat treatment at a high temperature and the shape formed after the development process is not kept and most of the irregularities of the embossing pattern are eliminated.
FIGS. 1A and 1B are cross-sectional views for the pattern obtained after development (FIG. 1A) and after thermal curing (FIG. 1B) when an embossing pattern is formed by using a conventional photoresist composition. On a substrate 10, a pattern 12 (in FIG. 1A) obtained after development and a pattern 12a (in FIG. 1B) after curing are illustrated. The curing was implemented at about 110xc2x0 C. for about 2 minutes and then at about 220xc2x0 C. for about 30 minutes. The pattern 12a after performing the curing process almost disappears due to flowing of the pattern by the applied heat. That is, the shape of the embossing pattern is not properly maintained. Accordingly, it would be highly desirable to develop a photoresist composition for forming a pattern of an organic insulating layer of which flowing can be restrained during implementing a thermal curing process and to provide a method of a patterning having a good profile after performing a thermal curing process.
A photoresist composition is provided, which includes about 100 parts by weight of an alkali-soluble acryl copolymer, about 5-100 parts by weight of 1,2-quinonediazide compound, about 2-35 parts by weight of nitrogen-containing cross-linker, and about 0.1-10 parts by weight of a thermal acid generator which produces an acid by heat.
According to an embodiment of the present invention, the alkali-soluble acryl copolymer has a weight-average molecular weight (Mw) in a range of about 5xc3x97103xe2x88x923xc3x97104 as converted to polystyrene. The alkali-soluble acryl copolymer is prepared by copolymerizing about 5-40% by weight of unsaturated carbonic acid, unsaturated carbonic acid anhydride or a mixture thereof, about 10-70% by weight of an epoxy-functional group containing unsaturated compound, and about 10-70% by weight of unsaturated olefin compound in a solvent having an polymerization initiator. The unsaturated carbonic acid is selected from the group consisting of acrylic acid, methacrylic acid, maleic acid anhydride, and their mixtures. The epoxy-functional group containing unsaturated compound is selected from the group consisting of glycidyl acrylate, glycidyl methacrylate, xcex1-ethylglycidyl acrylate, xcex1-n-propylglycidyl acrylate, xcex1-n-butylglycidyl acrylate, acrylic acid-xcex2-methyl glycidyl, methacrylic acid-xcex2-methyl glycidyl, acrylic acid-xcex2-ethyl glycidyl, methacrylic acid-xcex2-ethyl glycidyl, acrylic acid-3,4-epoxybutyl, methacrylic acid-3,4-epoxybutyl, acrylic acid-6,7-epoxy heptyl, methacrylic acid-6,7-epoxy heptyl, xcex1-ethyl acrylic acid-6,7-epoxy heptyl, o-vinylbenzyl glycidyl ether, m-vinyl benzylglycidyl ether, p-vinylbenzyl glycidyl ether, and their mixtures. The unsaturated olefin compound is selected from the group consisting of benzyl methacrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, t-butyl methacrylate, methyl acrylate, isopropyl acrylate, cyclohexyl methacrylate, 2-methyl cyclohexyl methacrylate, dicyclopentanyl oxyethyl methacrylate, isobornyl methacrylate, cyclohexyl acrylate, 2-methyl cyclohexyl acrylate, dicyclopentanyl oxyethyl acrylate, isovornyl acrylate, phenyl methacrylate, phenyl acrylate, benzyl acrylate, 2-hydroxyethyl methacrylate, styrene, xcex1-methyl styrene, m-methyl styrene, p-methyl styrene, vinyl toluene, p-methoxy styrene, 1,3-butadiene, isoprene, 2,3-dimethyl 1,3-budadiene, and their mixtures.
According to an embodiment of the present invention, the 1,2-quinonediazide compound is prepared by reacting a naphtoquinonediazide sulfonic acid halogen compound with a phenol compound under a presence of a base. The phenol compound is selected from the group consisting of 2,3,4-trihydroxy benzophenone, 2,4,6-trihydroxy benzophenone, 2,2xe2x80x2,4,4xe2x80x2-tetrahydroxy benzophenone, 2,3,4,3xe2x80x2-tetrahydroxy benzophenone, 2,3,4,4xe2x80x2-tetrahydroxy benzophenone, 2,3,4,2xe2x80x2-tetrahydroxy 4xe2x80x2-methyl benzophenone, 2,3,4,4xe2x80x2-tetrahydroxy 3xe2x80x2-methoxy benzophenone, 2,3,4,2xe2x80x26xe2x80x2-pentahydroxy benzophenone, 2,4,6,3xe2x80x2,4xe2x80x2,5xe2x80x2-hexahydroxy benzophenone, 3,4,5,3xe2x80x2,4xe2x80x2,5xe2x80x2-hexahydroxy benzophenone, bis(2,4-dihydroxyphenyl)methane, bis(p-hydroxyphenyl)methane, tri(p-hydroxyphenyl)methane, 1,1,1-tri(p-hydroxyphenyl)ethane, bis(2,3,4-trihydroxyphenyl)methane, 2,2-bis(2,3,4-trihydroxyphenyl)propane, 1,1,3-tris(2,5-dimethyl 4-hydroxyphenyl)-3-phenyl propane, 4,4xe2x80x2-[1-[4-[1-[4-hydroxyphenyl]-1-methylethyl]phenyl]ethylidene]bisphenol, bis(2,5-dimethyl 4-hydroxyphenyl)-2-hydroxyphenylmethane, and their mixtures. An esterification degree of the reaction between said naphthoquinonediazide sulfonic acid halogen compound and said phenol compound is in a range of about 50-85%.
According to an embodiment of the present invention, the 1,2-quinonediazide compound is at least one selected from the group consisting of 1,2-quinonediazide 4-sulfonic acid ester, 1,2-quinonediazide 5-sulfonic acid ester, and 1,2-quinonediazide 6-sulfonic acid ester. The nitrogen-containing cross-linking agent is at least one selected from the group consisting of methylol urea alkyl ether prepared by reacting a condensing product of urea and formaldehyde with alcohol, and methylol melamine alkyl ethers prepared by reacting a condensing product of melamine and formaldehyde with alcohol. The methylol urea alkyl ethers includes mono methyl urea methyl ether and dimethyl urea methyl ether, and the methylol melamine alkyl ethers includes hexamethylol melamine hexamethyl ether and hexamethylol melamine hexabutyl ether. The thermal acid generator includes a sulfonic ester compound.
The sulfonic ester compound is represented the following structure: 
wherein R represents alkyl group. The sulfonic ester compound includes cyclohexane toluene sulfonic ester having a structure (1), cyclohexane propyl sulfonic ester having a structure (2), cyclohexane methyl sulfonic ester having a structure (3), cyclohexane octyl sulfonic ester having a structure (4), and cyclohexane camphor sulfonic ester having a structure (5) 
The thermal acid generator is at least one selected from the group consisting of cyclohexanetoluene sulfonic ester, cyclohexanepropyl sulfonic ester, cyclohexanemethyl sulfonic ester, cyclohexaneoctyl sulfonic ester, and cyclohexanecamphor sulfonic ester. The thermal acid generator further includes about 50 parts by weight or less of a synthesizable compound having an unsaturated double bond based on 100 parts by weight of said alkali-soluble acryl copolymer, about 2 parts by weight or less of a surfactant based on 100 parts by weight of a solid content of said photoresist composition, and an adhesive. A solid concentration of said photoresist composition is in a range of about 30-70%.
A method of forming a pattern is provided, which includes the steps of: coating a photoresist composition on a substrate and drying to form a photoresist layer; exposing said photoresist layer by using a mask having a predetermined shape; developing the exposed photoresist layer by using an aqueous alkaline solution to form a photoresist pattern; and heating the photoresist pattern to cure thereof, wherein the photoresist composition comprises about 100 parts by weight of an alkali-soluble acryl copolymer, about 5-100 parts by weight of 1,2-quinonediazide compound, about 2-35 parts by weight of nitrogen-containing cross-linker and about 0.1-10 parts by weight of a thermal acid generator which produces an, acid by heat.
According to an embodiment of the present invention, the step of heating the photoresist pattern is performed at a temperature range of about 100xc2x0 C. to about 250xc2x0 C. The photoresist pattern is an embossing pattern of a liquid crystal display device.